Once-through vapor generating and superheating units



June 20, 1961 B. HAKE ETAL 2,989,036

ONCE-THROUGH VAPOR GENERATING AND SUPERHEATING UNITS J1 r 1 2151,/ 1260);@ (26e: m44

t 34.' as 38 42 INVENTORS rzzzard :ya/fe BY Joa Jegemazzrz ATTORNEY June 20, 1961 B. HAKE ElAL 2,989,036

ONCE-THROUGH VAPOR GENERATING AND SUPERHEATING UNITS Filed April 28, 1954 3 Sheets-Sheet 2 x, m m

w EL INVEN-roRs Bernhard :lfd/ce BY J0?? fgema/zm ATTORNEY June 20, 1961 B, HAKE ETA; 2,989,036

ONCEMTHROUGH VAPOR GENERATING AND SPERHEATING UNITS Filed April 28, 1954 5 Sheets-Sheet 3 FIG.5

INVENTORS wz/zard .azz/ak@ BY Johann Jzfegemann ATTORNEY nited States Patent ONCE-THROUGH VAPOR GENERATING AND SUPERI-IEATING UNITS Bernhard Hake, Dortmund-Kirchhorde, and Johann Hegemann, Ratingen, Germany, assignors to Durrwerke Aktiengesellschaft, Ratingen, Germany, a corporation of Germany Filed Apr. 28,1954, Ser. No. 426,198 5 Claims. (Cl. 122-235) This invention relates in general to the construction and operation of once-through forced circulation type vapor generating and superheating units. More specifically, the invention is concerned with the construction and arrangement of the fluid heating surface in a vapor generating and superheating unit of the character described which permits superheating of the generated vapor to a high temperatu-re and yet the location of the fluid heating zone in which the vapor-liquid mixture is converted to one hundred percent vapor in a relatively low heat input zone of the vapor generator.

Superheated steam, for example, is generated in a oncethrough forced circulation steam generator by the heating of water which is injected into one end of a ilow conduit and issues from the other end of the conduit as superheated steam. During the conversion of the water to steam there isa zone in which a steam-water mixture of predominantly steam content upon further heating becomes one hundred percent steam.- This zone is usually referred to the the transition zone. In once-through vapor generators internal scale tends to form or deposit in the transition zone. This scale creates a resistance to heat flow through the tube wall and tends to cause the tube metal temperature to rise above a safe operating temperature, thus increasing the probability of internal corrosion and tube failure. For this reason it has been customary to design such steam generating units so that this zone will be located in a relatively low temperature convection heat transfer section of the vapor generator. In such once-through steam generators, it is usual to place vapor generating tubes predominantly in the high heat input furnace area of the unit, and then to conduct the vaporliquid mixture from the furnace area to the low temperature convection heat transfer zone where the transition to steam occurs. When high steam temperatures are de sited, the steam is conducted to radiant superheating tubes in oradjacent to the furnace chamber. This arrangement requires the use of extensive iluid transfer pipes and additional headers which substantially increase the cost of such vapor generating units.

Furthermore, a convection heated transition zone cannot be limited to a small length of heated tube because as the vapor generating rate of the unit is either increased or decreased, the [transition occurring tends to shift either upstream or downstream respectively. This shifting of the transition zone causes the scale depositing or forming portion of the vapor generating tubes to be extensive in length. This long length of transition zone utilizes extensive amounts of low heat input conduit surface, thus further increasing the cost of the vapor generating unit.

In accordance with the present invention, the uid heating surface of a 'high temperature high capacity steam generating and superheating unit is constructed and arranged so that at least a major por-tion of the vapor generating tubes are arranged to receive their heat predominantly by radiation from the burning fuel stream in the furnace chamber, the vapor superheating tubes predominantly by radiation from the gases in a radiation chamber adjoining the furnace chamber and receiving heating gases directly therefrom, and the transition zone tubes predominantly by radiation from the lowest temperature section Y of the radiation chamber.

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This location of the transition zone minimizes the amount of expensive piping and headers required for connecting the high heat input steam generating and superheating tubes to the transition zone tubes, while providing all the uid heating tubes with most desirable heat transfer conditions to attain the desired heating effect.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which we have illustrated and described several embodiments of the invention.

In the drawings:

FIG. 1 is a schematic diagram of the liuid heating su face of a once-through forced circulation steam generating and superheating unit constructed in accordance with the invention, and showing a preferred arrangement of the radiant fluid heating surface with the four Vertical sides of the furnace chamber and adjoining radiation chamber being unfolded into 1a single vertical plane;

FIG. 2 is a vertical section of the unit shown in FIG. l looking towards the front wall;

FIG. 3 is a horizontal section taken on the line 3-3 of FIG. 2;

FIG. 4 is a horizontal section taken on the line 4--4 of FIG. 2; and i FIGS. 5, 6, and 7 illustrate modified arrangements of the uid heating surface.

The steam generating and superheating unit schematically illustrated has a vertical front wall 10, rear wall 12, and opposite side walls 14 and 16, defining a furnace chamber 18 and a vertically adjoining radiation chamber 20, broth of rectangular cross-section. The lower end of the furnace chamber is closed by a hopper 22. The furnace is fired by vertical rows 0f tangentially arranged uid fuel burners 24. The upper end of the radiation chamber opens into or is connected to the convection heating section of the unit (not shown) in which economizer and air heating surface may be located.

As shown in FIGS. 1 and 2, each of the furnace chambers walls is lined with panels of radiantly heated vertical steam generating tubes 26 extending between upper and lower horizontal headers and forming at least a major portion, if not all, of the entire steam generating surface of the unit, while the walls of the radiation chamber 20 are lined with radiantly heated tubes 30, 31 wound in horizontally extending groups or panels, each extending over portions of two adjacent walls of the radiation chamber. The furnace Wall tubes and headers are connected so as to form two parallel steam generating and superheating circuits, each consisting of half the tubes lining the front wall, the tubes lining one side wall, and half the tubes lining the rear wall. As shown, the feed water for each circuit enters a front wall bottom header 32 at a temperature below its boiling point, flows upwardly through tube group 26au to an upper header 33, downwardly through an unheated downcomer 35a to a bottom header 34, upwardly through side wall tube group 261J to upper header 35, downwardly through the downcomer 35b to bottom header 36, upwardly through tube group 26c to upper header 37, downwardly through downcomer 35c to bottom header 38, upwardly through tube group 26l to upper header 39, downwardly through downcomer 35d to bottom header 40, upwardly through tube group 26e to upper header 41, downwardly through downcomer 35e to bottom header 42, upwardly through tube group 26f to upper header 43, downwardly through downcomer 35f to lower header 44, the water and steam generated being well mixed in each transfer header. The mixture leaving the header 44 llows up- 3 wardly through the rear wall tube group 26g, the tubes of which are connected at their upper ends to corresponding tubes 30 lining the walls of the yradiation chamber 20.

The radiantly heated iluid heating tubes 30 lining the walls of the radiation chamber 20 are bent into sinuous nested formations having relatively short vertical runs and relatively long horizontal runs to form in effect horizontal tube groups or panels 30a, 30h, 30C, 30d, 30e, 30f, and 30g lining approximately half the rear wall and half one side wall of the radiation chamber and connected to provide ascending fluid flow through successive tube groups. The remaining half of the side wall and part of the front wall are lined with similar but reversely arranged tube groups 31a, 31", 31C, 31d, 31e, 31f, and 31S connected to provide a descending fluid tlow through successive tube groups. The lowermost tube group 31g is connected to a front wall group or panel 31h of vertical tubes leading to a common outlet header 42 at the upper end of the radiation chamber.

In accordance with the invention, the unit is so designed that during the expected load range of normal operation, the transition zone will be maintained within the portion of each circuit defined by the tube groups 30f, 30g, 31a, and 31h, and preferably within the tube groups 30g and 311 at the upper end of the radiation chamber. With this arrangement, the tube portions in the transition zone will be predominantly heated by radiation from the lowest temperature heating gases in the radiation chamber; an arrangement which permits these tubes to be heated at a higher heat input rate than if located in a convection heated section and yet maintained at `a safe temperature which will give a nal high steam superheat temperature at the outlet header 42.

The remaining tube ygroups 31C, 31d, 31e, 31f, 31g, 31h define the radiantly heated steam superheating section of each circuit, through which the steam flows downwardly, except in tube group 31h, counter currently to the upflowing stream of heating gases.

The placement of the transition zone in the heating gas exit end of an elongated radiation chamber has the advantage that the heating tubes presenting the transition zone are subjected to a minimum heat input. A further advantage is that the vapor generating tubes of the furnace walls and the superheating tubes are directly connected to the transition zone tubes and do not require expensive intermediate header members having long unheated connecting tubes which would be required if the transition zone were located in the heating gas convection zone of the unit.

As shown in FIGS. 5, 6 and 7, the unit may be constructed with a complete vapor generating and superheating circuit in each vertical wall of the furnace and radiation chambers. Also the vapor generating tube groups 126, 1261), 126C, and 126d may all be arranged for an upward flow of uid therethrough by means of outside downcomer tubes 135e, 135b and 135c externally connecting the upper header of one group to the bottom header of the adjoining tube group.

In FIG. the steam-water mixture flows upwardly through the tube group 126d, the tubes of which are connected at their upper ends to corresponding vapor generating tubes 130 lining the wall of the upper radiation chamber 20. The tubes 130 are bent into sinuous nested formations forming relatively short vertical runs and relatively long horizontal runs to form horizontal tube groups or panels 130g, 1301), 1300, 1301, 130e 130f and -130g lining approximately half of one wall of the radiation chamber and connected to provide ascending iluid flow through successive tube groups. The end portions of the tubes in group 130g are connected to corresponding tubes in the vapor superheating tube groups 131, which cover the remaining half of the wall of the upper radiation chamber 20. The tube ygroups 131 consist of a descending flow path in successive horizontal groups 131B', 1311 131C, 1311, 131e, 131f, and 131g.

4 The lowermost tube group 1312 passes through the chamber wall and is connected to an outlet header 42.

In this embodiment of the invention the transition zone occurs at the top of the radiation furnace chamber in tube groups 130f, 130g, 131% and 131", with the amount of pretransition zone surface inthe upper chamber being substantially equal to the amount of superheating surface. The superheating surface is arranged in a descending pattern and is exposed to constantly higher up flowing gas temperatures such that it may be described as a counterflow type radiant superheater.

In FIG. 6 the furnace chamber tubes 126 are arranged for fluid flow in the same manner `as in FIGURE 5. The steam-water mixture flows upwardly through the tube group 126d out of the furnace chamber and continues vertically along a wall of the upper radiation chamber 20 where the group connects to corresponding tube ends of the vapor generating tube group 130. The group 130 are formed into ascending horizontal nested formations of groups 1303, 130, and 130 which line a minor portion of a wall of the upper radiation chamber 20. The tubes of the group 130c are connected to corresponding superheating tubes of the group 131. Transition to one hundred per cent steam occurs in the horizontal tube groups 13011, 130C, 1311, and 131b with the steam preferably beginning to superheat in group 131e. 'Ihe superheater is composed of the short horizontal and descending How tube groups 131b, 131c and the long horizontal groups 1311, 131e, 1311, yand 131g which covers a major portion of a wall of the upper chamber 20. The lower tube group 131g passes through the wall of the upper chamber and is connected to the superheater steam outlet header 42.

The arrangement of vapor generator and superheater in FIGURE 6 is directed towards a unit which would deliver a high temperature superheated steam. In this embodiment of the invention vapor generating tubes cover a minor portion of a wall of the upper radiation chamber and the superheating tubes cover a major portion of said wall. Further, the arrangement of the vapor generating surface is in parallel-flow heat transfer relationship to heating gas flow and the major portion of the superheating Itubes being arranged in counter-How heat transfer relationship to the heating gas flow.

FIG. 7 illustrates an alternate superheater arrangement to that shown in FIG. 6. The transition zone occurs in tube group 1300, 130, 1311, and 131b exactly as in FIG. 6 and the steam is further superheated in the horizontal tube group 131e. Connected to the ends of the tube group 131c are corresponding tubes of tube group 231. The tube group 231 is composed of a vertical down low tube group 231d and long horizontal and ascending tube groups 231e, 231f, 231g, and 231k. The transition to percent steam will preferably occur in Itube group 131a with the steam then flowing in a descending or counter-now heat transfer relationship to a position in ythe lower part of the upper radiation chamber 20. The steam then ows in an ascending or parallel flow heat transfer relationship with the heating gases Vand leaves the vapor generator in the tube group 231h which is connected to the outlet steam heater 42.

The example of the invention shown in FIG. 7 is directed towards an arrangement of vapor generating and superheating tubes wherein the transition zone occurs in the low temperature por-tion of the upper radiation chamber 2,0 and the superheating tubes which cover a major portion of the wall of the chamber are arranged part in parallel-how and part in counter-ilow heat transfer relationship to the ilow of heating gases.

`In accordance with the spirit of this invention it may be readily understood that the embodiments described do not limit the application of the tube arrangements to tubes which line all of the walls of a radiation chamber nor to only one wall of a radiation chamber, but it is considered that the tube arrangements may be applied to any portion of the walls of the radiation chamber. It is also considered that the tubular arrangement shown may b e equally applicable for the heating of high temperature a1r.

While in accordance with the provisions of the statutes, there is illustrated and described herein specific forms of the lnvention, those skilled in the art will understand that changes may be made in the form of the invention covered by the claims, and that certain features of the lnvention may sometimes be used to advantage without a corresponding use of the other features.

What is claimed is:

1. In a tubular once-through forced circulation vapor generating and superheating unit having Walls defining a furnace chamber and an adjoining radiation chamber; means for burning fuel in said furnace chamber and causing a flow of heating gases from said furnace through said radiation chamber; means forming a heating gas outlet lfrom said radiation chamber; a plurality of parallel owing tubes disposed along the Walls of said chambers and arranged to receive heat primarily by radiation; said tubes comprising a vapor generating section, a transition zone section, and a vapor superheating section connected for serial fluid ow therethrough; said transition zone tubes being arranged to receive radiant heat primarily from the lowest temperature heating gas in said radiation chamber Iand the portion of said superheating section adjoining said transition zone section being arranged to receive radiant heat primarily from higher temperature gases than said transition zone.

2. In a tubular once-through forced circulation vapor generating and superheating unit having walls defining la rfurnace chamber and an adjoining radiation chamber; means for burning fuel in said furnace chamber and causing la ow of heating gases through said chambers; means forming a heating gas outlet from the portion of said radiant chamber most remote gas flow-wise from said fuel burning means; a plurality of parallel flowing tubes disposed `along the Walls of said chambers; and arranged to receive heat primarily by radiation, said tubes comprising a vapor generating section, a transition zone section, :and `a vapor superheating section connected for serial huid lllow therethrough; and said transition zone tubes being arranged adjacent said heating gas outlet `and the portion of said superheating section adjoining said transition zone arranged closer gas how-wise to said fuel burning means than said transition zone section.

3. In a tubular once-through forced circulation vapor generating and superheating unit having walls defining a lower vertically elongated furnace chamber and a vertically adjoining upper radiation chamber; means for burning lfuel in said furnace chamber and causing a how of heating gases through said chambers; means forming a heating gas outlet from the top of said radiation chamber; a plurality of parallel iowing tubes disposed along the 'walls of said chamber and arranged to receive heat primarily by radiation; said tubes comprising a vapor generating section, a transition zone section, and a vapor superheating section connected for serial fluid how therethrough; said vapor generating tubes disposed primarily in said furnace chamber; vapor generating tube extensions arranged in parallel ow heat transfer relationship to the heating gas flow along a part of the walls of the upper radiation chamber; said transition zone tubes positioned adjacent the heating gas outlet from said radiation chamber and arranged to receive heated fluid from said extensions While passing vapor to said superheater; and said superheating tubes positioned in said radiation chamber to receive radiant heat primarily from higher temperature gases than said transition zone tubes.

4. :In a tubular once-through forced circulation vapor generating and superheating unit having walls defining a lower vertically elongated furnace chamber and a vertically adjoining upper radiation chamber; meansfor burning fuel in said furnace chamber and causing a flow of heating ygases through said chambers; means forming a heating gas outlet from the top of said radiation chamber; a plurality of parallel -owing tubes disposed along the walls of said chambers; and arranged to receive heat primarily by radiation, said tubes comprising a vapor generating section, a transition zone section, and a vapor superheating section connected for serial fluid flow therethrough; said vapor generating tubes disposed primarily in said furnace chamber; vapor generating' tube extensions arranged in parallel iiow heat transfer relationship to the heating gas flow along substantially one half of the walls of the upper radiation chamber; said transition zone tubes positioned adjacent the heating gas outlet from said radiation chamber and arranged to receive heated fluid from said extensions while passing vapor to said superheater; said superheating tubes positioned along the remaining portion of said walls in said radiation chamber and arranged in counter ow heat transfer relationship to the heating gas flow to receive radiant heat primarily from higher temperature gases than said transition zone tubes.

5. In a tubular once-through forced circulation vapor generating and superheating unit having walls defining a lower vertically elongated furnace chamber and a vertically adjoining upper radiation chamber; means for burning fuel in said furnace chamber and causin ga ow of heating gases through said chambers; means forming a heating gas outlet from the top of said radiation chamber; a plurality of parallel flowing tubes disposed along the Walls of said chambers; and arranged to receive heat primarily by radiation, said tubes comprising a vapor generating section, a transition zone section, and a vapor superheating section connected for serial fluid ow therethrough; said vapor generating tubes disposed primarily in said furnace chamber; vapor generating tube extensions arranged in parallel flow heat transfer relationship to the heating gas flow along a minor portion of the walls of the upper radiation chamber; said transition zone tubes positioned adjacent the heating gas outlet from said radiation chamber and arranged to receive heated fluid from said extensions while passing vapor to said superheater; and said superheating tubes positioned along a major portion of the walls in said radiation chamber and arranged part in counter-W and part in parallel-flow heat transfer relationship to the heating gas flow to receive heat primarily from higher temperature gases than said transition zone tubes.

References Cited in the file of this patent UNITED STATES PATENTS Re. 19,977 Abendroth May 26, 1936 2,008,528 Warren July 16, 1935 2,074,235 Muller Mar. 16, 1937 2,526,339 Esnault-Pelterie Oct. 17, 1950 FOREIGN PATENTS 851,640 Germany Oct. 6, -2 

